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Why do blood type frequencies differ among human populations?

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Close-up illustration of multiple human red blood cells with their characteristic disc shape, floating against a red background. — blood group The major component of human blood is the red blood cell.

Blood type frequencies vary across human populations primarily due to the combined effects of natural selection and genetic drift.1

Natural Selection: Genetic variations in blood groups have evolved over time, partly because certain antigens may provide evolutionary advantages, such as resistance to specific diseases or infections. For example, the distribution of certain traits is linked to environmental pressures, such as the prevalence of malaria in specific geographic regions.1
Genetic Drift: In small or isolated populations, the frequency of certain alleles can change significantly by chance. If a small community experiences limited genetic diversity, specific blood group alleles may be lost or become more prevalent over generations. For instance, it is suggested that the B allele may have been lost by chance in some indigenous populations as their communities remained small.2

These evolutionary and demographic processes explain why, while all blood groups are found globally, their distribution remains distinct among different ethnic and geographic groups.2